The use of ketene dimer based agents in the paper industry to impart sizing, or water resistivity, to paper products is well known. Such agents are commercially available from Hercules Inc. Wilmington, Delaware under trade names such as AQUAPEL(copyright) and HERCON(copyright). Patents disclosing the compositions, variations and uses of these types of agents are:
The disclosures of which are incorporated herein by reference.
These sizing agents when added to the wet end of the paper machine, at the size press, or to the finished product in an off-machine application impart water resistivity to the paper, by decreasing the hydrophilicity of the sheet. The use of these sizing agents in writing paper, liner board, grocery bag and milk carton is well known, as all of these paper products require sizing.
These types of sizing agents are known to produce very hard sized (high resistivity to wetting) material such a milk carton. The use of these sizing agents in tissue and towel, although not unknown, has been very limited, because water resistivity is not desirable in these products. To the contrary, it has generally long been a goal in the tissue and towel industry to increase rather than decrease the rate at which the product is wetted and the total amount of water that the product can absorb. An example, however, of the use of ketene dimer sizing agents in tissue and towel products to increase water resistivity is found in European Patent Application No. 0 144 658 in the name of Dan Endres, assigned to Kimberly-Clark Corp.
It has been discovered that the use of deactivated ketene dimer sizing agents in tissue and towel increases the softness to these products while not materially effecting their water absorbtivity or hydrophilicity.
In one embodiment of this invention, a soft absorbent tissue product comprising long and short paper making fibers and a having hydrolyzed ketene dimer agent is provided. A soft absorbent paper product comprising paper making fibers and at least about 1 pound per ton of a hydrolyzed ketene dimer agent, the tissue having an absorbency rate test of less than about 50 seconds is further provided.
In an additional embodiment of the invention, a soft absorbent tissue sheet comprising a first layer and a second layer with the first layer comprising predominantly long paper making fibers and the second layer comprising predominantly short paper making fibers is provided. At least one of these layers further comprises a ketene dimer and this layer is readily wetable by water. This soft tissue may be creped or through dried. It may also have an absorbency rate test less than about 10 seconds.
In yet a further embodiment of the invention, a soft paper product having paper making fibers and at least about 1 pound per ton of fiber of a ketene dimer sizing agent that has been neutralized so that the product has an absorbency test of less than about 40 seconds is provided.
In still another embodiment of the invention, a paper sheet having improved softness comprising a first sheet surface and a second sheet surface and having a layer comprising paper making fibers is provided. The layer has a surface that corresponds to a surface of the paper sheet. The surface of the layer has a deactivated ketene dimer sizing agent therein so that the wetability of the sheet is equivalent to a sheet of similar composition but not having the deactivated ketene dimer sizing agent therein. This paper sheet may be a bath tissue having a second layer comprising paper making fibers, or be a towel product. This sheet may also be a facial tissue with two or more layers comprising paper making fibers. The sheet may also be a three layer sheet.
An additional embodiment of the present invention is a paper sheet having improved softness comprising cellulose paper making fibers and a hydrolyzed ketene dimer agent in which the sizing of the sheet is no greater than about three times the sizing of a sheet of similar composition but not having the hydrolyzed ketene dimer agent.
In an alternative embodiment of the invention, a method is provided for making a soft absorbent paper sheet product having improved softness. This method comprises forming in a pulper an aqueous slurry comprising paper making fibers, hydrolyzing a ketene dimer sizing agent, combining the product of the hydrolyzation of the ketene dimer sizing agent with the paper making fibers, and removing the water from the aqueous slurry to form a paper sheet. In this method, the product of the hydrolyzation of the ketene dimer may be combined with the paper making fibers either prior to, during or after the removal of water from the slurry.
In yet another embodiment of the invention a soft highly absorbent blended base sheet having a deactivated ketene dimer sizing agent is provided. This blended base sheet may have long and short paper making fibers.